Marine mammal distribution in Ecuador: surveys aboard a ship of opportunity as a means of monitoring relative abundance

Abstract

Five marine mammal surveys between 2008 and 2011 were conducted aboard the Buque de Investigación Orion (the research vessel for the Oceanographic Institute of the Ecuadorian Navy) within oceanic waters adjacent to mainland Ecuador and the Galápagos Islands. The surveys dedicated extensive time in deep, offshore waters where cetaceans were not densely present. Sightings of 12 species were compared with an earlier survey aboard the B/I Orion in 2001 as well as with a subset of published data from three NOAA STAR (Stenella Abundance Research) surveys between 1999 and 2003. Additionally, a small boat, near-shore survey, was conducted during June 2010 among andnear the Galápagos Islands. Encounter rates ranged annually from 0.012 cetacean/km to 0.027 cetacean/km. The highest encounter rate aboard the B/I Orion took place during the April 2009 survey. In order to compare sightingrates between the B/I Orion and NOAA platforms, the average effective half-strip widths were used to determine encounter rates per area effectively searched. A zonation within the study region was observed between odontocete andbalaenopterid cetaceans as well as between striped (Stenella coeruleoalba) and short-beaked common dolphins (Delphinus delphis). Several methodological aspects of surveys and geographical features that may influence encounter rates and subsequent abundance estimates are discussed. This study demonstrates that vessels of opportunity provide a valuable means of studying open-ocean and coastal distributions of marine mammals. Possible methodological improvements, such as the use of high-power binoculars, that could increase the absolute number of sightings, the efficiency of these opportunistic surveys, and improve the sighting rates of more evasive species are discussed.

Bryde’s whales (Balaenoptera brydei) in an area of upwelling off Isla San Cristóbal, Galápagos

“…In Galápagos, Bryde's whales are typically solitary but they have also been observed in groups of two to three individuals [3]. O'Hern et al [4] reported seeing Bryde's whales in summer 2010 while surveying for marine mammals and tuna-dolphin-bird aggregations along the north coast of Isla San Cristóbal in the Galápagos Marine Reserve (GMR). During this study, Bryde's whales were observed more frequently along the north coast of San Cristóbal (nine sightings) than along the south coast (two sightings), even though most of the island margin area from SW to NE along the north coast is orographically blocked from the SE Trade Winds that promote wind-induced upwelling elsewhere in Galápagos.…”

Spatiotemporal relationships of threatened cetaceans and anthropogenic threats in the lower Yangtze system

“…Although distance sampling is widely used for estimating cetacean abundances and distribution patterns, this approach could not be employed in our study because we were forced to follow a restricted survey route in Poyang Lake. However, encounter rates are also widely used to understand relative abundance and distribution patterns for cetaceans (Dan, 1988;O'Hern et al, 2014;Marcoux et al, 2016;Moore and Barlow, 2017;Rone et al, 2017) and investigate spatial relationships between cetaceans and threats (Braulik et al, 2018). Estimation of encounter rates has also been the primary survey method for previous porpoise monitoring in Poyang Lake, with population trends for 2006-2017 based on encounter rate analysis (Zhao, 2009;Huang et al, 2020).…”

Priorities for ecological research on cetaceans in the Galápagos Islands

“…Long-term outcomes (years to decades) Target species Unlike pinnipeds, for which population assessments have been conducted on a regular basis throughout Galaṕagos (e.g., Paéz-Rosas et al, 2021), very few studies have reported population assessments for cetaceans in Galaṕagos (Palacios and Forney, 2008;O'Hern et al, 2017;Whitehead and Shin, 2022), and there is no formal ongoing program for monitoring cetacean populations. Yet, baseline information on demographic parameters, such as density, abundance, survival, and recruitment, is essential for understanding population status and dynamics, and to unravel the relative importance of competition and predation in structuring the local cetacean community relative to the influences of environmental variability.…”

“…A long-term study of sperm whales in Galaṕagos waters began in the mid 1980s, which has provided the basis for much of the contemporary knowledge on the species (e.g., Whitehead, 2003;Eguiguren et al, 2021). Several other research expeditions have been undertaken in Galaṕagos with the explicit purpose of studying cetaceans since then (Lyrholm et al, 1992;Smith and Whitehead, 1999;Palacios, 1999a;Palacios, 2000;Wise et al, 2009;Feĺix et al, 2011;Biggs et al, 2017;O'Hern et al, 2017). With the establishment of the GMR, since the early 2000s collaborative efforts between Galaṕagos-based and international scientists have continued to generate crucial knowledge about marine mammals in the area (Palacios and Salazar, 2002;Palacios et al, 2004;Denkinger et al, 2013;Biggs et al, 2017;O'Hern et al, 2017;Eguiguren et al, 2019;Denkinger et al, 2020;Eguiguren et al, 2021;Paéz-Rosas et al, 2021).…”

“…Several other research expeditions have been undertaken in Galaṕagos with the explicit purpose of studying cetaceans since then (Lyrholm et al, 1992;Smith and Whitehead, 1999;Palacios, 1999a;Palacios, 2000;Wise et al, 2009;Feĺix et al, 2011;Biggs et al, 2017;O'Hern et al, 2017). With the establishment of the GMR, since the early 2000s collaborative efforts between Galaṕagos-based and international scientists have continued to generate crucial knowledge about marine mammals in the area (Palacios and Salazar, 2002;Palacios et al, 2004;Denkinger et al, 2013;Biggs et al, 2017;O'Hern et al, 2017;Eguiguren et al, 2019;Denkinger et al, 2020;Eguiguren et al, 2021;Paéz-Rosas et al, 2021). Finally, cetacean presence in Galaṕagos has also been gleaned from documentation of live-stranding events, beach-cast specimens, and osteological specimens in museums (Palacios, 1996;Palacios et al, 2004).…”